For acronyms up to four letters long, we use all capital letters: NATO, for instance. But for acronyms of five letters or more, we just capitalize the first letter, as in Nafta or Unicef. That's because a story filled with long, all-cap expressions looks strange on the page, as though someone were shouting at you: NAFTA, I say! NAFTA, NAFTA, NAFTA!

Nobody else follows the four caps rule. I think it has more to do with how well you know the word and whether you're aware it's an acronym or have got used to treating it as an opaque word.

The argument that serial commas were not used in newspapers to save typesetting fails to account for the fact that there is no consensus on their use (I tend to follow the reasonable line that if there is no ambiguity the deciding factor is the length of the items in the list).